In general, because a minor in most cases cannot initiate or defend lawsuits without adult assistance, a court will appoint a guardian ad litem for a minor appearing in court in order to ensure that the minor's interests are adequately represented. While parents usually serve as the guardian, a guardian ad litem may be appointed if a parent or general guardian is unavailable, incompetent, or has conflicting interests.

Any person, including non-lawyers, may be appointed to serve in the capacity of a guardian ad litem. Some states have mandatory training in order to qualify as a guardian ad litem, while other states have no training or standards. Various terms exist for guardians ad litem, including Court Appointed Special Advocate, law guardian, or next friend.

Guardians ad litem perform various functions depending upon the state and type of court. In general, they serve one of three purposes: (1) to protect a child's "best interests"; (2) to be an independent fact-finder for the judge; or (3) to follow and advocate the child's wishes. The appointment of guardians ad litem are generally considered to be within the discretionary powers of the court.

They are often appointed in adoption, child custody, child support, paternity, visitation rights, and child abuse cases. Guardians ad litem have also been appointed to represent the interests of unborn heirs who are beneficiaries to a trust, in cases involving wills and trusts, and when a child has an interest in an insurance policy or some other benefit.